is it a white fluffy fungus? if it is it might be wooly aphid. an insecticide that is designed to get through the 'wool' will be effective. or use a systemic insecticide. try watering less and from the bottom, keeping the stems dry.

Thanks Seaburngirl. Yes it is white fluffy fungus. I shall try an insecticide and water from the bottom, although I don't expect to be watering to often at this time of year. Many thanks again!
Bbjsparky.

scrape a bit off and see if there is an insect/grub in it. if there is it needs the insecticide if not there isnt any need to spray with insecticide. try a fungicide.